1. Field of the Invention
The present invention relates generally to a display for use with a computer or the like type of device and more specifically to a so called clear blue circuit for use with such a display or monitor which improves the clarity and visibility of blue characters.
2. Description of the Prior Art
It is widely accepted that characters which are displayed in blue monochromatic color exhibit reduced visibility as compared with those displayed in green. In an attempt to overcome this problem a prior art arrangement shown in FIG. 3 has been proposed. In this arrangement the red (R), green (G) and blue (B) digital signals which have been supplied from the computer to the display interface, are subject to simple digital-analog conversion by b/A converters 101R, 101G and 101B to form analog output signals R, G and B.
In this instance each of these circuits includes a resistor dividing circuit. A logic circuit 102 determines the presence of a blue signal when a blue signal appears in the absence of red and green signals. This circuit improves the visibility of the blue characters by inducing the D/A converters 101R and 101G to output red and green signal in a predetermined ratio with respect to the blue signal. In other words, the circuit mixes a little red and green into the blue to improve clarity.
However, this circuit is incapable of processing analog RGB input. Further, the digital RGB signals can have either 8 or 16 color levels. On the other hand, analog RGB signal can have essentially an infinite number of levels or graduations. Accordingly, the above type of circuit is such that the logic circuit is incapable of distinguishing between pure blue and a blue which contains some red or green.